Tire non-uniformity relates to the symmetry (or lack of symmetry) relative to the tire's axis of rotation in mass, geometric or stiffness characteristics. Conventional tire building methods unfortunately have many opportunities for producing non-uniformities in tires. During rotation of the tires, non-uniformities present in the tire structure produce periodically-varying forces at the wheel axis. Tire non-uniformities are important when these force variations are transmitted as noticeable vibrations to the vehicle and vehicle occupants. These forces are transmitted through the suspension of the vehicle and may be felt in the seats and steering wheel of the vehicle or transmitted as noise in the passenger compartment. The amount of vibration transmitted to the vehicle occupants has been categorized as the “ride comfort” or “comfort” of the tires.
Many different factors can contribute to the presence of non-uniformities in tires, even when the tires are built under seemingly identical process conditions. Examples of such factors include the location of product start points and/or joint overlap locations for one or more of the many complex tire building products and/or steps. Exemplary products include the casing textile plies, the belt plies, bead rings, the inner liner, the tread and other rubber layers. Steps involving these and other products include the application of such products to a form or drum, placing the resulting green structure in a mold or press and subjecting the structure to heat and pressure to shape and cure the rubber products and bond the materials into an integrated unit.
Tire uniformity characteristics, or parameters, are generally categorized as dimensional or geometric variations (radial run out (RRO) and lateral run out (LRO)), mass variation or uneven mass distribution, and rolling force variations (radial force variation, lateral force variation and tangential force variation, sometimes also called longitudinal or fore and aft force variation). Measuring one or more of the above parameters at high speed provides high speed uniformity (HSU) characteristics for a tire. Uniformity measurement machines often calculate the above and other uniformity characteristics by measuring force with a load cell located either at the tire hub or in a road wheel or the like.
One type of uniformity parameter that is of particular interest in the automotive industry corresponds to radial force variations at generally high speeds, such as those in excess of about 25 mph. Many tire manufacturers have started implementing or are being pressured to implement HSU control by addressing high speed radial force variation (HSRFV). Direct measurement of tire HSU parameters, including HSRFV, however, has been difficult and quite costly, making industrial control rather difficult. To avoid the expense and difficulty associated with direct high speed uniformity measurement in the factory setting, some in the tire industry have focused on predicting HSU by correlating more readily accessible low speed uniformity (LSU) measurements to various HSU attributes. These correlations have ranged on a continuum from purely phenomenological to purely statistical in nature, but many have had only limited success.
One known attempt at predicting tire HSU is disclosed in U.S. Pat. No. 5,396,438 (Oblizajek), which predicts HSU based on multiple low speed parameters such as radial run out (RRO), instantaneous rolling radius (IRR), and radial force variation (RFV) as obtained on low speed uniformity machines.
Yet another example related to aspects of high speed uniformity is found in U.S. Pat. No. 6,065,331 (Fukasawa), which predicts higher order components of high speed uniformity based on low speed uniformity measurements.
Another known technique for predicting and controlling tire HSU is disclosed in U.S. Pat. No. 7,082,816 (Zhu), owned by the present Applicant. In the Zhu '816 patent, technology is disclosed for characterizing both uneven mass distribution and high speed uniformity of a tire based on a functional model derived by representing a tire as a generally circular flexible ring. Although this approach has proven value, the functional model employed in the Zhu '816 patent can sometimes be difficult to implement in practice. In addition, such model does not account for certain aspects of crown deformation. Still further, modeling the tire as a simple ring fails to account for differences in tire structure and performance over a range of lateral locations across a tire crown. Finally, such model sometimes lacks flexibility and ease of implementation because it is locked into a phenomenological model with various parameter assumptions tied thereto.
Although known technology for characterizing tire high speed radial force variation and uneven mass distribution and affecting associated aspects of tire manufacturing have been respectively developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.